float acoshf(float x);

acoshf returns the non-negative inverse hyperbolic cosine of x.

acosh(x) is defined as log(x + sqrt(x^2 − 1)), assuming completely accurate computation.

If x < 1, errno is set to EDOM and acoshf returns HUGE_VALF.

If x < 1, acoshf returns NaN.
If x is NaN, acoshf returns that NaN.